Influence of site factors and vascular conductivity on the development of procerum root disease

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Abstract

Procerum root disease (PRD) is a serious problem in eastern white pine (Pinus strobus
L.) Christmas tree plantations in VIrginia. Procerum root disease is caused by Leptographium
procerum (Kendr.) Wingf which is believed to be transmitted by the pales weevil Hylobius
pales (Herbst). Symptoms of procerum root disease include reduced shoot elongation,
reduced leaf conductance, low photosynthetic activity, low pre-dawn water potential and
chlorosis of foliage. Resinous occlusion of the sapwood at the root collar is the likely cause
of the suite of symptoms that resemble water stress. Increased incidence ofPRD has been
associated with trees growing in poorly drained soils in low lying areas. Two studies were
undertaken to explore the relationship of site factors and vascular conductivity of sapwood
to the expression ofPRD symptoms in P. strobus. In the first study, plots were established
in a variety of drainage classes in two Christmas tree plantations. Leaf conductance was
monitored periodically in conjunction with measurements of soil factors to assess the role of
abiotic factors on foliar symptom expression. At the termination of the field monitoring, trees
were harvested and three vascular disease severity variables were measured: hydraulic
conductivity of sapwood, percent basal occlusion and sapwood moisture content. These
disease severity variables describe the permeability of sapwood to water and the relative hydration of the sapwood. Reduced leaf conductance was associated with reduced stem
hydraulic conductivity, reduced sapwood moisture content and increased basal occlusion.
Increased vascular disease severity and foliar symptom expression were associated with
increased soil moisture content and several other factors that relate to soil moisture retention
(percent slope, total porosity, textural class and bulk density). The second study was initiated
to study the development of PRD in artificially inoculated P. strobus seedlings exposed to
three soil water classes: droughty, optimum and saturated. Seedlings in the optimum soil
water class exhibited the greatest biomass accumulation and shoot elongation, while seedlings in droughty showed the least. No negative effects of L. procerum inoculation and no
symptoms ofPRD were observed eight months after inoculation regardless of the soil water
class.
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